Although they're ranked No. 1 in the NFL in total defense this season, aging Pittsburgh unit hopes to keep improving

Is this the year their aging defense finally kicks the bucket? How will they survive without the face of the defense in the huddle every Sunday? Can they get their once-feared pass rush back?

Sound familiar?

Since they reported for training camp in late July, the Pittsburgh Steelers have had to defend themselves against similar questions to the ones that have dogged the Ravens (7-2) over the past 3 1/2 months. But unlike their AFC North rivals from Baltimore, whom they will host at Heinz Field on Sunday night, the Steelers (6-3) have come up with better answers.

"We don't let that get to us. We can't care what people say," starting cornerback Keenan Lewis said. "Everybody is going to have something to say to us. But that's all they are, just opinions."

The historically stingy Steelers haven't just survived without perennial Pro Bowl safety Troy Polamalu, and with other veteran defenders, such as safety Ryan Clark and sack-happy outside linebackers James Harrison and LaMarr Woodley battling injuries — they actually continue to thrive, despite the fact they will likely start seven 30-something defenders Sunday.

The Steelers rank first in the league in total defense, pass defense and yards allowed and seventh in scoring defense, carrying on the tradition of a unit that has dominated the NFL since 2008.

Over the past five seasons, the Steelers have allowed a league-low 16.2 points per game and an NFL-fewest 271.9 yards per game (the Ravens rank second and third in those categories, respectively).

They say they have been able to keep it going thanks to contributions from younger defenders such as Lewis, inside linebacker Lawrence Timmons and defensive end Ziggy Hood. Lewis has knocked down a team-high 19 passes. Timmons had the game-turning interception in Monday's win over the Kansas City Chiefs. Hood is doing his best to replace Aaron Smith, who retired before this season.

"It's the mentality here. It's always the next guy up. There can't be [any] drop-off," Steelers nose tackle Casey Hampton said Friday. "The Steelers don't bring a lot of [marquee] free agents in. We bring in guys and put them through the system. The next guy up has usually been in the system for a few years and knows what he is doing. That helps out a lot when we have injuries."

Sound familiar?

The Ravens have been ravaged by injuries — and a few key free-agent departures — but they are still waiting for young players such as defensive end Pernell McPhee, nose tackle Terrence Cody and outside linebacker Paul Kruger to become consistent contributors. Another recent draft pick who has disappointed, cornerback Jimmy Smith, is now sidelined after sports hernia surgery.

With inside linebacker and emotional leader Ray Lewis and cornerback Lardarius Webb on injured reserve and Pro Bowl defensive tackle Haloti Ngata and outside linebacker Terrell Suggs trying to play through injuries, the Ravens rank 27th in yards allowed and are 13th in scoring defense. They have just 16 sacks, but have averaged two takeaways per game.

Like that proud Ravens unit, the Steelers also believe they have plenty of things to fix if they are to get back to playing the brand of smothering defense on which they built their reputation.

The Steelers are tied with the Ravens and two other teams for 22nd in sacks. Only one team has forced fewer than the Steelers' nine takeaways, something that has been a regular topic of discussion in Pittsburgh's meeting rooms this week. And they are in the middle of the pack in third-down defense and red-zone defense, two areas that could be the difference in Sunday's showdown.

"We had quite a few young players who were taking on a larger role. I think they're growing and some of the guys that are coming back in are getting their football reactions better," Steelers defensive coordinator Dick LeBeau said. "But teams should get better as you go through the year. We hope we have a lot of improvement in front of us. We sure need to get better."

Harrison and Woodley, two recent tormentors of the Ravens, are back after missing games earlier in the season, though they have combined for just four sacks. Clark, a Pro Bowler for the first time in 2011, has suffered concussions in two of his last three games, but says he has been cleared to play Sunday. Polamalu, who has only played in two games, has been ruled out.

"We've had some injuries, but every team goes through that," defensive end Brett Keisel said.

Polamalu, whose long curly black hair is the most iconic aesthetic of the Steelers defense, has made many pivotal plays in this rivalry, like his interception return for a touchdown in the 2008 AFC championship game and his soaring strip-sack of Ravens quarterback Joe Flacco two seasons ago. But with Polamalu sidelined by a nagging calf injury, the Steelers are struggling to recreate that kind of chaos.